There are numerous electronic components which, during use, become heated, i.e., act as "heat sources", in response to internal electric power dissipation. Solid state and other current-carrying devices generate internal heat during use. If the heat is not promptly removed, the device's internal temperature rises to unacceptable levels at which thermally induced failure may occur. Where such devices are used in expensive or defense-related equipment, it is extremely important to avoid such failures. There is, therefore, a need for heat sink units attachable to such devices to continually remove heat generated therein and to dissipate it to the ambient atmosphere. Optionally, such devices include means for directing a flow of air or other suitable fluid at or past the heat source and the attached heat sink unit.
Preferably, heat is continuously removed by thermal conduction from at least a portion of such a heat source. The heat is removed by intimate contact between a portion of the heat sink unit and a corresponding portion of the heat source, and the thermally conducted heat must then be removed from the heat sink unit. Heat removal from the heat sink can be efffected by known techniques, e.g., by radiation, by free or forced gas convection, or by free or forced liquid convection.
Typically, a heat exchanger surface is attached in a conventional manner to an outermost surface of the heat source and, during use, acts as a thermal transformer. In essence, the heat exchanger surface transforms the problem of removing heat from a high power density condition at a first surface (as at a surface of the heat producing device) to removing heat from a second surface having a lower power density (as at the relatively large surface area of the heat exchanger exposed to the ambient atmosphere). Such a thermal transformation reduces the power density at the final heat dissipating surface to a level that can be handled, especially where convection is relied upon, at reasonable, slower coolant velocities for any ambient coolant flow contacting the final cooling surface.
Quite apart from the fundamental problem of how to attach a heat sink unit to a heat source in the present context, the degree of contact obtainable between the heat source surface and the heat sink surface across the contact interface is known to be highly dependent on the "actual" contact surface area as distinguished from the "nominal" contact or interface area of the two abutting bodies. One known solution for facilitating heat conduction between the abutting interface surfaces is to insert a thermally conductive deformable material between them. Such a material may, for example, be a conductive paste, commonly known as a "heat sink compound", that is applied as a very thin layer at the interface between the contacting surfaces. While this is helpful, it has been found that increasing the compressive force with which the heat sink and the heat source surfaces make contact at the interface increases the "actual" contact area significantly and that this has a much more pronounced effect on the rate at which heat is transferred across a nominal unit area of the interface.
Numerous configurations have been attempted to forcibly clamp or otherwise hold together a heat sink unit to a heat source. A common problem, however, is that most such devices undergo thermal cycling and possibly vibration or mechanical shock during use. In normal use of the known structures, the force that holds a heat sink unit to a heat source generally decreases with time. Incidental trauma suffered by a cooled device during use, in the known art, has a tendency to reduce heat transfer efficiency of the device.
There is, therefore, a definite need for an improved heat sink unit that can be forcibly attached to a heat source, wherein the heat sink unit, during use of the device, grips the heat source with increasing force as the combination is subjected to thermal and mechanical shock, vibration, or other incidental experiences during use.